1. Field of the Invention
This invention relates to a speech processor unit for an auditory prosthesis. More particularly, the invention relates to an external speech processor unit for a cochlear implant system.
2. Related Art
Hearing loss, which may be due to many different causes, is generally of two types, conductive and sensorineural. In some cases, a person may have hearing loss of both types. Conductive hearing loss occurs when the normal mechanical pathways for sound to reach the hair cells in the cochlea are impeded, for example, by damage to the ossicles. Conductive hearing loss is often helped by use of conventional hearing aids which amplify sound so that acoustic information reaches the cochlea and the hair cells.
In many people who are profoundly deaf, however, the reason for their deafness is sensorineural hearing loss. This type of hearing loss is due to the absence of, or destruction of, the hair cells in the cochlea which transduce acoustic signals into nerve impulses. These people are thus unable to derive suitable benefit from conventional hearing aid systems, no matter how loud the acoustic stimulus is made, because there is damage to, or absence of, the mechanism for nerve impulses to be generated from sound in the normal manner.
It is for this purpose that cochlear implant systems have been developed. Such systems bypass the hair cells in the cochlea and directly deliver electrical stimulation to the auditory nerve fibres, thereby allowing the brain to perceive a hearing sensation resembling the natural hearing sensation normally delivered to the auditory nerve.
Typically, cochlear implant systems consist essentially of two components, an external component commonly referred to as a processor unit and an internal, implanted component commonly referred to as a stimulator/receiver unit, the latter receiving signals from the processor unit to provide the sound sensation to a user.
The external component includes a microphone for detecting sounds, such as speech and environmental sounds, a speech processor that converts speech into a coded signal, a power source such as a battery, and an external transmitter coil.
The coded signal output by the sound processor is transmitted transcutaneously to the implanted stimulator/receiver unit situated within a recess of the temporal bone of the user. This transcutaneous transmission occurs via the external transmitter antenna coil which is positioned to communicate with an implanted receiver antenna coil of the stimulator/receiver unit. Therefore, the communication serves two essential purposes; firstly to transmit, transcutaneously, the coded signal and, secondly, to provide power to the implanted stimulator/receiver unit. The transcutaneous link is, normally, in the form of a radio frequency (RF) link, but other such links have been proposed and implemented with varying degrees of success.
The implanted stimulator/receiver unit includes, in addition to the receiver antenna coil that receives the coded signal and power from the external processor component, a stimulator that processes the coded signal and outputs a stimulation signal to an intracochlea electrode assembly which applies the electrical stimulation directly to the auditory nerve producing a hearing sensation corresponding to the originally detected sound.
The external component is carried on the body of the user, such as in a pocket of the user's clothing, a belt pouch or in a harness, while the microphone is mounted on a clip mounted behind the ear or on the lapel of the user.
More recently, the physical dimensions of the sound processor have been able to be reduced allowing for the external component to be housed in a relatively small unit capable of being worn discreetly behind the ear of the user. The external transmitter antenna coil is still positioned on the side of the user's head to allow for the transmission of the coded sound signal and power from the sound processor to the implanted stimulator unit.
Such behind the ear units (BTEs) have provided a degree of freedom and subtlety for the recipient which has not traditionally been possible with body worn devices. There is no longer a need for extensive cables connecting the body worn processor to the transmitter antenna coil, nor is there a need for a separate microphone unit or battery pack, as the BTE unit contains all the components in one housing.
One common feature of all BTE units is the provision of a dedicated mechanical switch for turning the unit on or off. Such a switch is typically small in size and difficult to manipulate, especially in the case of elderly recipients or those who are not very dexterous. Continuous use of the switch causes mechanical fatigue resulting in the switch failing to operate and requiring repair or replacement.
A further problem with BTE devices of current designs is that the area around the switch permits the ingress of moisture that can damage or destroy the device.
Any discussion of documents, acts, materials, devices, articles or the like which has been included in the present specification is solely for the purpose of providing a context for the present invention. It is not to be taken as an admission that any or all of these matters form part of the prior art base or were common general knowledge in the field relevant to the present invention as it existed before the priority date of each claim of this application.